Is boiler underspec?

[bruba]

Hi all

I recently had a heat only boiler fitted with a spec of 18kw. I have a Edwardian 4-bedroom house with high ceilings largish rooms and 11 radiators.

The two previous quotes recommended a 24kw boiler.

The house seems to take a while to heat to say 21c and I am using quite a bit of Gas.

Speaking to Worcester Bosch, they advised a minimum of 21kw.

Your thoughts?

Thanks in advanced.

 

[Jackrae]

Did you go for a cheaper quote, if so you probably got what you paid for.
How exactly do you know you are "..using quite a bit of Gas."
The gas consumption rate is a function of the boiler rating so a 24kw unit could be expected to consume around 33% more than an 18kw unit when burning at full chat.
Your boiler installer will have checked the gas burn rate (hopefully) as part of the commissioning procedure to confirm the boiler was firing correctly.
An under-sized boiler will obviously take longer to get radiators and hence room space up to temperature, but at the end of the day the amount of gas consumed should balance out. ie heat generated by boiler versus heat lost to outside ambient is a function of differential temperature.
Bear in mind that a cooler thermostat setting will cut your gas usage.

 

[bruba]

Thanks for your response.

Did you go for a cheaper quote, if so you probably got what you paid for.
No the quote was more expensive, it was grant funded.

How exactly do you know you are "..using quite a bit of Gas."
Higher cost than the previous boiler and the house doesn't get as hot or at least takes hours longer.

The gas consumption rate is a function of the boiler rating so a 24kw unit could be expected to consume around 33% more than an 18kw unit when burning at full chat.
But if a boiler is under spec, would it not work harder and have to stay on longer using more gas?

Your boiler installer will have checked the gas burn rate (hopefully) as part of the commissioning procedure to confirm the boiler was firing correctly.

Not if they are maximizing profits.

An under-sized boiler will obviously take longer to get radiators and hence room space up to temperature, but at the end of the day the amount of gas consumed should balance out. ie heat generated by boiler versus heat lost to outside ambient is a function of differential temperature.

I am not technical, but the manufacturer recommended a minimum 21kw.

 

[Jackrae]

Gas consumption is measured in cubic metres not £ Price of gas has gone up in recent months !

So why did you go for a more expensive undersized boiler in contradiction to the design spec.

The tax payer helped buy your boiler and now you're complaining ?

 

[bruba]

Gas consumption is measured in cubic metres not £ Price of gas has gone up in recent months !
Correct, that is how I measured the usage.

So why did you go for a more expensive undersized boiler in contradiction to the design spec.
The other two quotes were before I was approved for the grant,

The tax payer helped buy your boiler and now you're complaining ?
I have a disability and a vulnerable person, not complaining,

I asked a technical question on the correct forum in which you seemed to have answered in the second sentence. You sound very toxic get back into your box sir!

A toxic person is anyone whose behavior adds negativity and upset to your life. Many times, people who are toxic are dealing with their own stresses and traumas. To do this, they act in ways that don't present them in the best light and usually upset others along the way!

 

[JonathanM]

Do you know what spec your old boiler was?

Do you have a room thermostat?

Is the boiler accessible? Can you see the display on the front? If so, there might be some basic checks you can do.

 

[flameport]

The two previous quotes recommended a 24kw boiler

Based on what?

A heat loss calculation for the rooms in the building should have been done first, so that the boiler could be sized appropriately.
If that wasn't done, then the boiler was sized entirely by guessing, the installation won't comply with building regulations, and isn't likely to work as intended.

 

[Jackrae]

My question was quite polite, but I cannot help how you interpret it ?

The boiler will only burn gas at the rate specified by its design. For example, in 10 hours an 18Kw unit will (if running non-stop and with no modulation) consume 180kw hours of gas putting X amount of heat into the house. For a 24kw unit to put in the same amount of heat it would run for 18/24 of the time and effectively consume the same amount of gas.

The main difference between the 2 boiler ratings is that the smaller boiler simply takes longer to get things warmed up.

As an analogy you could liken it to filling a bathtub from a 1/2" valve rather than a 3/4" valve. One takes longer than the other but the same amount of water is used.

 

[Bouy]

If it eventually it heats the house to your desired temperature then it must be sized correctly i.e. heat in = heat out. How fast you want it to get up to temp is another factor.

 

[Mister Banks]

My question was quite polite, but I cannot help how you interpret it ?

The boiler will only burn gas at the rate specified by its design. For example, in 10 hours an 18Kw unit will (if running non-stop and with no modulation) consume 180kw hours of gas putting X amount of heat into the house. For a 24kw unit to put in the same amount of heat it would run for 18/24 of the time and effectively consume the same amount of gas.

The main difference between the 2 boiler ratings is that the smaller boiler simply takes longer to get things warmed up.

As an analogy you could liken it to filling a bathtub from a 1/2" valve rather than a 3/4" valve. One takes longer than the other but the same amount of water is used.

Whilst your calculations are valid they don’t take into account that the bath has a small leak half way up the side! So the smaller valve never fills the bath whereas the larger valve eventually does. Houses leak heat in a similar way.

 

[bruba]

Thanks for your input all.

As Mr Banks mentions, I interpret that as ..

I would of thought you would factor in whether property had loft insulation, wall insulation etc or even the EPC rating of the house?

The house struggles to heat past 21c

I'm not technical hence posting question on here.

Thanks

 

[JonathanM]

What temperature is the boiler set at?

 

[bruba]

55C

 

[old duffer]

heat input per room = desired room temp - heat loss per room
If you don't know what you need then how can you decide what the max input requirement is?

 

[oldbutnotdead]

Were any radiators replaced when the boiler was installed? Have you tried not heating the whole house? (if you don't have any modern control gear, just turn off 2 or 3 less needed radiators (usually bedrooms) at the start of a heating period, see if/how quickly the heated areas achieve temperature.
EDIT Did your previous quotes include any heatloss calcs for the house?
EDIT 2- This is a problem with heating grants- you the end user get little or no say in what boiler is installed- you'll get the cheapest or whatever the installer had kicking about that's close enough.